1. Field of the Invention
The present invention relates to a vacuum booster apparatus and a brake apparatus including a vacuum booster.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 8-164840 discloses a vacuum booster apparatus provided with a vacuum booster. The vacuum booster comprises a first pressure chamber which is connected to an intake line of an engine at a position downstream of a throttle valve and a second pressure chamber which is selectively connectable to either the first pressure chamber or atmosphere. The vacuum booster boosts an operational force applied to a brake-operating member based on a difference between a pressure in the first pressure chamber and a pressure in the second pressure chamber. The vacuum booster apparatus also includes a throttle-opening-degree control apparatus which increases a negative pressure in the first pressure chamber by decreasing a degree of opening of the throttle valve. In the above-mentioned vacuum booster apparatus, when the negative pressure in the first pressure chamber becomes less than a predetermined negative pressure, the degree of opening of the throttle valve is decreased so as to maintain the negative pressure in the first pressure chamber at a pressure higher than the predetermined negative pressure. Accordingly, since the negative pressure in the first pressure chamber is maintained higher than the predetermined negative pressure whether or not the brake-operating member is being operated, a boost limit is prevented from being decreased. The boost limit is represented by a master cylinder pressure at a time when a boost action reaches a limit.
The above-mentioned engine having the throttle valve is a direct-injection-type gasoline engine in which gasoline is directly injected into cylinders. In this type of engine, a uniform combustion is performed when a load applied to the engine is large, that is, when an engine speed is high. On the other hand, when a load applied to the engine is not very large, that is, when the engine speed is medium or low, a stratified charge combustion is performed. In the uniform combustion, a combustion is achieved at a normal air-fuel ratio, that is, a stoichiometric air-fuel ratio. In the stratified charge combustion, an ultra lean burn occurs at a high air-fuel ratio of about 25 to 50. According to the ultra lean burn, a rate of fuel consumption is reduced which results in energy saving. When the engine load is medium or low, a necessary drive torque can be output even when the ultra lean burn occurs. Since, normally, the engine load is not very large when the brake operating member is being operated, the ultra lean burn is performed. In such the case, a degree of opening of the throttle valve is maintained at a relatively large degree so as to intake a large amount of air.
If the degree of opening of the throttle valve is maintained at a relatively large degree, the negative pressure in the first pressure chamber tends to be decreased. Accordingly, in the conventional vacuum booster apparatus, the degree of opening of the throttle valve is decreased when the negative pressure in the first pressure chamber is less than the predetermined negative pressure. When the degree of opening of the throttle valve is decreased, a state of combustion should be changed from the ultra lean burn to the uniform combustion. This is because an unstable combustion causing misfire occurs when the degree of opening of the throttle valve is decreased. Additionally, the change from a state of the ultra lean burn to a state of the uniform combustion is performed stepwisely (gradually). If an output torque is the same, an amount of injection of fuel, the degree of opening of the throttle valve and a degree of opening of a swirl port are considerably different between the state of the ultra lean burn and the state of the uniform combustion. Accordingly, when the state of the ultra lean burn is changed to the uniform combustion, these conditions are considerably changed, which results in deterioration of drivability. Similarly, the return from the state of the uniform combustion to the state of the ultra lean burn is performed stepwisely. As mentioned above, when the degree of opening of the throttle valve is decreased when the ultra lean burn is being performed, it is required to stepwisely or gradually change the ultra lean burn to the uniform combustion. This causes deterioration in a rate of fuel consumption. Accordingly, it is not preferable to decrease the degree of opening of the throttle valve so as to maintain a negative pressure in the first pressure chamber in a state in which the ultra lean burn is performed. Additionally, a frequency of such a change in the state of combustion should be as small as possible. On the other hand, when a braking operation is not being performed, there is a possibility that the uniform combustion is performed. In such a case, the rate of fuel consumption is not decreased by much even if the degree of opening of the throttle valve is decreased.
If the predetermined negative pressure at which the degree of opening of the throttle valve is decreased can be decreased, that is, if the predetermined negative pressure can be set closer to an atmospheric pressure, a frequency of the degree of opening of the throttle valve being decreased can be decreased. However, in such a case, the limit of boost is decreased. On the other hand, if the predetermined negative pressure is increased, that is, if the predetermined negative pressure is set closer to an absolute vacuum, the limit of boost can be increased. That is, the boosting function can be provided until an operational force applied to the brake-operating member is large. However, in such a case, the frequency of a degree of opening of the throttle valve being decreased is increased. Additionally, since the vacuum booster cannot reach the limit of boost even if the negative pressure is less than the predetermined negative pressure in a range where an operational force applied to the brake-operating member is small, the degree of opening of the throttle valve is decreased despite that the negative pressure is not required to be increased. As discussed above, in the above-mentioned vacuum booster apparatus, it is difficult to decrease a frequency of the degree of opening of the throttle valve being decreased while a necessary negative pressure is maintained in the first pressure chamber.
In the above-mentioned patent document, a vacuum booster apparatus which can decrease the frequency of the degree of opening of the throttle valve being decreased during a braking operation is also disclosed. This vacuum booster apparatus includes the above-mentioned vacuum booster and a throttle-valve-opening control apparatus. The throttle-valve-opening control apparatus increases a negative pressure in the first pressure chamber by decreasing the degree of opening of the throttle valve when the brake-operating member is continuously operated for a period longer than a predetermined period and when the negative pressure in the first pressure chamber is less than the predetermined negative pressure. In this vacuum booster apparatus, the degree of opening of the throttle valve is always decreased when the brake-operating member is continuously operated for a period longer than the predetermined period and when the negative pressure in the first pressure chamber is less than the predetermined negative pressure. However, when an operational force applied to the brake-operating member is small, the vacuum booster does not reach the limit of boost even if the braking operation continues for a long time and the negative pressure is small. In such a case, the negative pressure is not required to be increased. Additionally, when the operational force is large, the vacuum booster may reach the limit of boost even if the braking operation continues for only a short time. In such a case, the negative pressure should be increased. As discussed above, in the above-mentioned vacuum booster, the degree of opening of the throttle valve may be unnecessarily decreased or not decreased when it is required.
It is a general object of the present invention to provide a vacuum booster apparatus and a brake apparatus in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a vacuum booster apparatus and a brake apparatus which positively decreases a degree of opening of a throttle valve when it is required while an unnecessary decrease in the degree of opening of the throttle valve is positively prevented.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a vacuum booster apparatus adapted to be used for a brake apparatus provided in a vehicle having an internal combustion engine, the vacuum booster apparatus comprising:
a vacuum booster having a first pressure chamber and a second pressure chamber, the first pressure chamber being connected to an intake pipe of the engine on a downstream side of a throttle valve, the second pressure chamber being selectively connectable to one of the first pressure chamber and atmosphere, the vacuum booster boosting an operating force applied to a brake operating member based on a pressure difference between the first pressure chamber and the second pressure chamber; and
a throttle-opening-degree control device controlling a negative pressure in the first pressure chamber by controlling a degree of opening of the throttle valve,
wherein the throttle-opening-degree control device includes limited-time opening-degree decreasing means for decreasing the degree of opening of the throttle valve only for a limited time when the negative pressure in the first pressure chamber is smaller than a predetermined necessary negative pressure determined by an operating force relating amount related to the operatingforce applied to the brake operating member.
According to the present invention, the operating force relating amount is related to the operating force applied to the brake operating member such as a brake pedal. That is, the operating force relating amount includes the operating force itself and an amount in which the operating force is reflected such as a travel of the brake operating member or a master cylinder pressure.
In the vacuum booster apparatus according to the present invention, the predetermined necessary negative pressure is determined in accordance with the operating force relating amount that relates to the operating force applied to the brake operating member. That is, the predetermined necessary negative pressure is stepwisely or gradually increased as the operating-force relating amount is increased. Additionally, the degree of opening of the throttle valve is decreased only when the negative pressure in the first pressure chamber is smaller than the predetermined necessary negative pressure.
The vacuum booster is closer to its boost limit when the operating-force relating amount is large than when the operating-force relating amount is small. Accordingly, when the operating-force relating amount is large, the negative pressure in the first pressure chamber is preferably increased so as to increase a boost limit of the vacuum booster so that the vacuum booster is prevented from reaching its boost limit. On the other hand, when the operating force relating amount is small, there is no need to increase the boost limit. That is, it is not required to increase the negative pressure in the first pressure chamber. According to the vacuum booster apparatus of the present invention, since the predetermined necessary negative pressure is determined in accordance with the operating-force relating amount, the degree of opening of the throttle valve can be decreased only when it is necessary.
In the vacuum booster apparatus according to the present invention, the limited-time opening-degree decreasing means may include necessary-negative-pressure determining means for determining the predetermined necessary negative pressure in accordance with an operating-force relating amount related to the operating force applied to the brake operating member.
The predetermined necessary negative pressure may be determined by the operating-force relating amount alone or with other conditions of a braking operation such as a period of operating the brake operating member and a rate of increase in the operating-force relating amount.
Additionally, in the vacuum booster apparatus according to the present invention, the limited-time opening degree decreasing means may include means for determining the predetermined necessary negative pressure in accordance with a rate of increase in an operating-force relating amount related to the operating force applied to the brake operating member.
According to this invention, the predetermined necessary negative pressure is determined according to the operating force relating amount and the rate of increase in the operating-force relating amount. That is, the predetermined necessary negative pressure is increased as the rate of increase is increased. Thus, if the operating-force relating amount is the same, the predetermined necessary negative pressure when the rate of increase in the operating force relating amount is large is set to be greater than when the rate of increase in the operating-force relating amount is small.
When the rate of increase in the operating-force relating amount is large, a rate of evacuation of air in the first pressure chamber is preferably increased so as to maintain an appropriate operational speed of the vacuum booster. On the other hand, when the rate of increase in the operating-force relating amount is small, there is no need to increase the predetermined necessary negative pressure. Accordingly, when the operating-force relating amount is the same, the predetermined necessary negative pressure when the rate of increase in the operating-force relating amount is large is preferably set to be greater than when the rate of increase in the operating force relating amount is small.
Additionally, the rate of increase in the operating force relating amount is set to be a large value when it is required to rapidly decrease a speed of a vehicle. In such a case, a possibility for the vacuum booster reaching it boost limit is high. Thus, it is preferable to increase the negative pressure in the first pressure chamber. On the other hand, when the rate of increase in the operating-force relating amount is small, the possibility for the vacuum booster reaching its boost limit is low. In this case, there is no problem if the negative pressure in the first pressure chamber is small. Particularly, when an operating force applied to the brake operating member is released, the rate of increase in the operating-force relating amount becomes a negative value. In this case, the possibility for the vacuum booster reaching its boost limit is low. That is, a margin to the boost limit when the rate of increase in the operatingforce relating amount is large is smaller than when the rate of increase in the operating-force relating amount is small.
Additionally, in the vacuum booster apparatus according to the present invention, the limited-time opening degree decreasing means may decrease the degree of opening of the throttle valve only when a boost limit of the vacuum booster is smaller than an operational state value which is determined according to an operating-force relating amount related to the operating force applied to the brake operating member.
The boost limit of the vacuum booster is equal to the master cylinder pressure at a time when a boost action of the vacuum booster reaches its limit. Accordingly, the operational state value can be the master cylinder pressure as the operating force relating amount at that time. Additionally, the operational state value can be set as other values such as the operating-force applied to the brake operating member corresponding to the master cylinder pressure or a travel of the brake operating member. Further, the operational state value can be a value determined by the operating-force relating amount and the rate of increase in the operating force relating amount.
The boost limit of the vacuum booster is determined by a pressure difference between the first pressure chamber and the second pressure chamber when the pressure in the second pressure chamber reaches an atmospheric pressure. The boost limit is increased as the pressure difference is increased. The pressure difference is increased as the negative pressure in the first pressure chamber is increased. Accordingly, the boost limit is increased as the negative pressure in the first pressure chamber is increased. A level of the negative pressure in the first pressure chamber needed for increasing the boost limit to be greater than the operational state value is determined by a level of the operational state value, and such a negative pressure is referred to as a boosting-time necessary minimum negative pressure. If the degree of opening of the throttle valve is decreased only when the boost limit is smaller than the operational state value, the negative pressure in the first pressure chamber can be maintained to be greater than the boosting-time necessary minimum negative pressure. Thus, measures should be taken for a decrease in the degree of opening of the throttle valve only when the negative pressure in the first pressure chamber is smaller than the boosting-time necessary minimum negative pressure.
Additionally, there is provided according to another aspect of the present invention a vacuum booster apparatus adapted to be used for a brake apparatus provided in a vehicle having an internal combustion engine, the vacuum booster apparatus comprising:
a vacuum booster having a first pressure chamber and a second pressure chamber, the first pressure chamber being connected to an intake pipe of the engine on a downstream side of a throttle valve, the second pressure chamber being selectively connectable to one of the first pressure chamber and atmosphere, the vacuum booster boosting an operating force applied to a brake operating member based on a pressure difference between the first pressure chamber and the second pressure chamber; and
a throttle-opening-degree control device controlling a degree of opening of the throttle valve in accordance with a negative pressure in the first pressure chamber and at least one of an operating-force relating amount related to the operating force applied to the brake operating member and a rate of increase in the operating-force relating amount.
In the vacuum booster apparatus according to this invention, the degree of the throttle valve is controlled based on the negative pressure in the first chamber and at least one of the operating-force relating amount and the rate of increase in the operating-force relating amount. For example, the degree of opening of the throttle valve may be decreased when the negative pressure in the first pressure chamber is smaller than a preset negative pressure and when the operating-force relating amount is greater than a preset amount, or when the operating-force relating amount is greater than a preset amount and the rate of increase in the operating-force relating amount is greater than a preset rate. In any case, the degree of opening of the throttle valve is decreased only when the negative pressure in the first pressure chamber is required to be increased. Thus, a frequency of operations for decreasing the degree of opening of the throttle valve can be decreased.
Additionally, there is provided according another aspect of the present invention a vacuum booster apparatus adapted to be used for a brake apparatus provided in a vehicle having an internal combustion engine, the vacuum booster apparatus comprising:
a vacuum booster having a first pressure chamber and a second pressure chamber, the first pressure chamber being connected to an intake pipe of the engine on a downstream side of a throttle valve, the second pressure chamber being selectively connectable to one of the first pressure chamber and atmosphere, the vacuum booster boosting an operating force applied to a brake operating member based on a pressure difference between the first pressure chamber and the second pressure chamber; and
a throttle-opening-degree control device controlling a negative pressure in the first pressure chamber by controlling a degree of opening of the throttle valve,
wherein the throttle-opening-degree control device includes large-change-time opening degree decreasing means for decreasing the degree of opening of the throttle valve as a rate of increase in an operating-force relating amount related to the operating force applied to the brake operating member is increased.
The negative pressure in the first pressure chamber needed to be increased more when the rate of increase in the operating-force relating amount is large as compared to when the rate of increase is small.
In the conventional vacuum booster apparatus, the degree of opening of the throttle valve is decreased when an operation of the brake operating member continues longer than a preset time and when the negative pressure in the first pressure chamber is smaller than a preset negative pressure. However, when a rapid braking operation is performed, that is, when the rate of increase in the operating force relating amount is large, the negative pressure in the first pressure chamber must be increased even if the operation of the brake operating member continues a short time. Yet, in such a case, the degree of opening of the throttle valve is not decreased. n the other hand, when the rate of increase in the operating-force relating amount is small, that is, for example, when the operating force applied to the brake operating member is released (the rate of increase is a negative value), the degree of opening of the throttle valve is decreased although the negative pressure in the first pressure chamber could be small. In order to eliminate such an inconvenience, in the vacuum booster apparatus according to this invention, the degree of opening of the throttle valve when the rate of increase in the operating-force relating amount is large is decreased more than when the rate of increase in the operating force relating amount is small. Thus, the degree of opening of the throttle valve is decreased only when it is necessary.
In the above-mentioned invention, the throttle-opening-degree control device may further include increasing-rate-related limited-time opening-degree decreasing means for decreasing the degree of opening of the throttle valve only for a limited time when the negative pressure in the first pressure chamber is smaller than a predetermined necessary negative pressure determined according to the rate of increase in the operating-force relating amount.
Additionally, there is provided according to another aspect of the present invention a vacuum booster apparatus adapted to be used for a brake apparatus provided in a vehicle having an internal combustion engine, the vacuum booster apparatus comprising:
a vacuum booster having a first pressure chamber and a second pressure chamber, the first pressure chamber being connected to an intake pipe of the engine on a downstream side of a throttle valve, the second pressure chamber being selectively connectable to one of the first pressure chamber and atmosphere, the vacuum booster boosting an operating force applied to a brake operating member based on a pressure difference between the first pressure chamber and the second pressure chamber; and
a throttle-opening-degree control device controlling a negative pressure in the first pressure chamber by controlling a degree of opening of the throttle valve,
wherein the throttle-opening-degree control device includes operating-time opening-degree-decrease suppressing means for suppressing a decrease in the degree of opening of the throttle valve so that the decrease in the degree of opening of the throttle valve when the brake operating member is being operated is smaller than when the brake operating member is not being operated.
When a braking operation is being performed, the second pressure chamber is alternately connected to either the first pressure chamber or atmosphere. Accordingly, the negative pressure in the first pressure chamber is decreased as the braking operation continues. If the negative pressure in the first pressure chamber is sufficiently increased before the braking operation is performed, that is, when a braking operation is not being performed, the negative pressure in the first pressure chamber can be maintained at a sufficient level for a long time. That is, the negative pressure in the first pressure chamber can be prevented from being smaller than the predetermined necessary negative pressure if the negative pressure in the first pressure chamber is increased when a braking operation is not being performed. Accordingly, a frequency of operations for decreasing the degree of opening of the throttle valve can be deceased when a braking operation is being performed.
As discussed above, if the degree of opening of the throttle valve is decreased when a braking operation is being performed, that is, the ultra lean burn is performed, a rate of fuel consumption is increased. However, according to the vacuum booster apparatus of this invention, since a frequency of operations for decreasing the degree of opening of the throttle valve is decreased, an increase in the rate of fuel consumption can be suppressed.
Additionally, when the negative pressure in the first pressure chamber is increased when a braking operation is being performed, a braking force is increased if the operating force applied to the brake operating member by a driver is constant. In order to maintain a constant braking force, the driver must control the operating force. This deteriorates a brake feel given to the driver. In order to eliminate such an inconvenience, in the vacuum booster apparatus according to this invention, a frequency of operations for decreasing the degree of opening of the throttle valve is decreased so that the operation for decreasing the degree of opening of the throttle valve is rarely performed when a braking operation is being performed. Thus, there is an advantage in that deterioration of a braking feel is prevented.
In the vacuum booster apparatus according to the above-mentioned invention, the throttle-opening-degree control device may include opening-degree decreasing means for decreasing the degree of opening of the throttle valve when the negative pressure in the first pressure chamber is smaller than a preset negative pressure, and the operating-time opening-degree-decrease suppressing means may include operating-time preset-negative-pressure decreasing means for decreasing the preset negative pressure so that the preset negative pressure when the brake operating member is being operated is smaller than that when the brake operating member is not being operated.
When a braking operation is not being performed, the degree of opening of the throttle valve is decreased when the negative pressure in the first pressure chamber is smaller than a non-operating-time preset negative pressure. When a braking operation is being performed, the degree of opening of the throttle valve is decreased when the negative pressure in the first pressure chamber is smaller than an operating-time preset negative pressure, which is smaller than the non-operating-time preset negative pressure. Since the operating-time preset negative pressure is smaller than the non-operating-time preset negative pressure, a start condition to start a decreasing operation for the degree of opening of the throttle valve when a braking operation is being performed tends to be unsatisfied as compared to that when a braking operation is not being performed. That is, a frequency of operations for decreasing the degree of opening of the throttle valve is decreased since the non-operating-time preset negative pressure is set to be a relatively large value.
Each of the operating-time preset negative pressure and the non-operating-time preset negative pressure may be either a fixed value or a variable value determined according to an operational state of the brake operating member.
For example, the operating-time preset negative pressure may be set to a value at which the vacuum booster does not reach its boost limit when the brake operating member is operated by a normal operating force, and the non-operating-time preset negative pressure may be set to a value at which the vacuum booster does not reach its boost limit even when the negative pressure in the first pressure chamber becomes small due to the brake operating member being operated by a normal operating force. In such a case, the non-operating-time preset negative pressure is set to be greater than the operating-time preset negative pressure by an amount of decrease in the negative pressure when a normal braking operation is performed.
Additionally, the operating-time preset negative pressure may be set to the above-mentioned predetermined necessary negative pressure. The non-operating-time preset negative pressure may be a fixed value or a variable value. For example, the non-operating-time preset negative pressure may be set to a value greater than a maximum operating-time preset negative value during a previous braking operation by the above-mentioned amount of decrease in the negative pressure when a normal braking operation is performed. Additionally, the non-operating-time preset negative pressure may be set to a value corresponding to a running state of the vehicle. That is, the non-operating-time preset negative pressure when a vehicle speed is large may be set to be greater than that when the vehicle speed is low, or the non-operating-time preset negative pressure when a vehicle is running up a slope may be set to be greater than that when the vehicle is running down a slope.
Additionally, in the vacuum booster apparatus according to the above-mentioned invention, the operating-time preset-negative-pressure decreasing means may include operating-time preset-negative-pressure determining means for determining the preset negative pressure used when the brake operating member is being operated in accordance with at least one of an operating-force relating amount related to the operating force applied to the brake operating member and a rate of increase in the operating-force relating amount.
When a braking operation is being performed, the degree of opening of the throttle valve is decreased only when the negative pressure in the first pressure chamber is smaller than the operating-time preset negative pressure (hereinafter referred to as a variable preset negative pressure) which is determined based on at least one of the operating-force relating amount and the rate of increase in the operating-force relating amount. When the variable preset negative pressure is smaller than the operating-time preset necessary negative pressure (hereinafter referred to as a fixed preset negative pressure) which is previously determined as mentioned above, a frequency of operations for decreasing the degree of opening of the throttle valve can be further decreased.
Additionally, the operating-time preset negative pressure may be selectively set to one of the variable preset negative pressure and the fixed preset negative pressure. For example, if the degree of opening of the throttle valve is decreased when the negative pressure in the first pressure chamber becomes smaller than the one of the variable preset negative pressure and the fixed preset negative pressure which is greater than the other, the vacuum booster can be prevented from reaching its boost limit when the brake operating member is being operated with a large operating force. In such a case, the fixed preset negative pressure can be determined to be a minimum negative pressure in the first pressure chamber.
Additionally, there is provided according to another aspect of the present invention a brake apparatus adapted to be provided in a vehicle having an internal combustion engine, the brake apparatus comprising:
a vacuum booster having a first pressure chamber and a second pressure chamber, the first pressure chamber being connected to an intake pipe of the engine on a downstream side of a throttle valve, the second pressure chamber being selectively connectable to one of the first pressure chamber and atmosphere, the vacuum booster boosting an operating force applied to a brake operating ember based on a pressure difference between the first pressure chamber and the second pressure chamber;
a braking-force assisting apparatus increasing a braking force to a value greater than a value corresponding to an output of the vacuum booster; and
a throttle-opening-degree control device controlling a degree of opening of the throttle valve, the throttle-opening-degree control device including abnormal-time throttle-opening-degree decreasing means for decreasing the degree of opening of the throttle valve, when an abnormality occurs in the braking force assisting apparatus, so as to increase a negative pressure in the first pressure chamber.
In the above-mentioned invention, the braking-force assisting apparatus may increase a braking force after the vacuum booster reaches its boost limit or before the vacuum booster reaches its boost limit. As for the braking-force assisting device which increases a braking force before the vacuum booster reaches its boost limit, there is a type which increases a braking force when an emergency braking operation is performed and a type which increases a braking force a predetermined period before the vacuum booster reaches its boost limit. If the vacuum booster is a type in which a boost ratio changes before the vacuum booster reaches its boost limit, a braking force is increased at a time when the boost ratio is changed. In any case, in a brake apparatus provided with a braking-force assisting apparatus, a necessity for decreasing the degree of opening of the throttle valve is high when an abnormality occurs in the braking-force assisting apparatus, and is low when the braking-force assisting apparatus is normal.
The braking-force assisting apparatus may comprise a reservoir, a pump which pressurizes the brake fluid in the reservoir and provides the pressurized brake fluid to a brake cylinder, a motor for driving the pump, a pressure control device which can control the fluid pressure in the brake cylinder by the brake fluid discharged by the pump and braking-force controlling means for controlling the fluid pressure in the brake cylinder by controlling the motor and the pressure control device. When an abnormality occurs in the motor or the pressure control device, or when the an abnormality occurs in an electric system such as in the braking-force controlling means, it is determined that an abnormality occurs in the braking-force assisting apparatus. An abnormality occurring in the braking-force assisting apparatus can be detected by an abnormality detecting device.
A description will now be given of a case in which a braking force is increased after the vacuum booster reaches substantially an atmospheric pressure.
When the braking-force assisting apparatus is normal, a braking force can be increased after the vacuum booster reaches its boost limit. However, when an abnormality occurs in the braking force assisting apparatus, a braking force cannot be increased. In such a case, the boost limit of the vacuum booster can be increased by increasing the negative pressure in the first pressure chamber. If the brake operating member is operated with a large operating force, the vacuum booster is prevented from reaching its boost limit and the operating force is boosted by the vacuum booster which results in an increase in the braking force. On the other hand, when the braking-force assisting apparatus is normal, the braking force can be increased after the vacuum booster reaches its limit without increasing the boost limit of the vacuum booster. Thereby, the negative pressure in the first pressure chamber is not required to be increased.
When the braking-force assisting apparatus is abnormal, the degree of opening of the throttle valve may be decreased when the negative pressure in the first pressure chamber is smaller than the preset negative pressure, or may be decreased either when the negative pressure in the first pressure chamber is smaller or greater than the preset negative pressure. The above-mentioned preset negative pressure may be a predetermined fixed value or a variable value which is determined by the operating-force relating amount related to the operating force applied to the brake operating member.
The braking-force assisting apparatus may be any apparatus which increases a braking force after the vacuum booster reaches its boost limit. That is, the braking-force assisting apparatus may be an apparatus which increases a braking force to a value corresponding to an operating force applied to the brake operating member, or may be an apparatus which increases a braking force independent of an operating force applied to the brake operating force. Additionally, the fact that the vacuum booster has reached its boost limit can be detected by a boost-limit detecting device which detects the pressure in the second pressure chamber having reached an atmospheric pressure or detects the master cylinder pressure having reached a boost limit which can be obtained according to the negative pressure in the first pressure chamber.
It should be noted that even in the brake apparatus according to the present invention, a decrease of the degree of opening of the throttle valve cannot be completely omitted when the braking-force assisting apparatus is normal. When the braking force assisting apparatus is abnormal, the degree of opening of the throttle valve is decreased due to an abnormality occurring in the braking-force assisting apparatus. The degree of opening of the throttle valve may be decreased, when the braking-force assisting apparatus is normal, due to other causes such as a case in which the negative pressure in the first pressure chamber is smaller than the predetermined necessary negative pressure which is determined according to the operating-force relating amount related to the operating force applied to the brake operating force. In such a case, when the braking-force assisting apparatus is abnormal, the degree of opening of the throttle valve is decreased by the abnormal-time throttle opening degree decreasing means, and when the braking-force assisting apparatus is normal, the degree of opening of the throttle valve is decreased by the limited-time opening-degree decreasing means. In a case in which a braking force is increased after the vacuum booster reaches its boost limit, if the boost limit is increased when the braking force assisting apparatus is normal, a frequency of the vacuum booster reaching its boost limit can be decreased which results in a decrease in a frequency of operation of the braking-force assisting apparatus.
In the brake apparatus according to the present invention, the braking-force assisting apparatus may increase the braking force after a pressure in the second pressure chamber reaches substantially an atmospheric pressure, and the abnormal-time throttle-opening-degree decreasing means may determine the degree of opening of the throttle valve in accordance with a target boost limit.
According to this invention, the degree of opening of the throttle valve which degree is decreased when the braking-force assisting apparatus is abnormal, is determined by the abnormal-time throttle-opening-degree determining means. During an abnormal time in which the throttle valve is maintained at a degree of opening, the negative pressure in the first pressure chamber when the abnormal-time throttle opening degree is small can be greater than that when the abnormal-time throttle opening degree is large. That is, the abnormal-time throttle-opening degree when the target boost limit (corresponds to the negative pressure in the first pressure chamber) is large is determined to be smaller than that when the target boost limit is small.
Additionally, together with or instead of the abnormal-time throttle opening degree, a decreased-state maintaining time which is a period for maintaining a state in which the degree of opening of the throttle valve is small may be determined. A level of the negative pressure in the first pressure chamber is not increased, immediately after the degree of opening of the throttle valve is decreased, to a level corresponding to the degree of opening of the throttle valve. Accordingly, the negative pressure in the first pressure chamber and the boost limit when the decreased-state maintaining time is long is greater than that when the decreased-state maintaining time is short. In such a case, the abnormal-time throttle-opening-degree decreasing means includes opening-degree decreased-state-maintaining determining means.
In the brake apparatus according to the present invention, the braking-force assisting apparatus may increase the braking force after a pressure in the second pressure chamber reaches substantially an atmospheric pressure, and the abnormal-time throttle-opening-degree decreasing means decreases the degree of opening of the throttle valve when the negative pressure in the first pressure chamber is smaller than a predetermined necessary negative pressure which is determined in accordance with at least one of an operating-force relating amount related to the operating force applied to the brake operating member and a rate of increase in the operating-force relating amount.
In the brake apparatus according to this invention, the degree of opening of the throttle valve is decreased when the braking-force assisting apparatus is abnormal and when the negative pressure of the first pressure chamber is smaller than the predetermined necessary negative pressure. That is, if the braking-force assisting apparatus is abnormal, the negative pressure in the first pressure chamber is not required to be increased when the vacuum booster does not reach its boost limit or when a possibility for the vacuum booster reaching its boost limit is low. Thus, in the brake apparatus according to the present invention, a frequency of operations for decreasing the degree of opening of the throttle valve can be decreased.
Additionally, in the brake apparatus according to the present invention, the abnormal-time throttle-opening-degree decreasing means may decrease the degree of opening of the throttle valve when the brake operating member is not being operated and when the negative pressure in the first pressure chamber is smaller than a non-operating-time preset negative pressure, and the abnormal-time throttle opening degree decreasing means may also decrease the degree of opening of the throttle valve when the brake operating member is being operated and when the negative pressure in the first pressure chamber is smaller than an operating-time preset negative pressure which is smaller than the non-operating-time preset negative pressure.
As mentioned above, the degree of opening of the throttle valve does not have to be decreased immediately after an abnormality occurs in the braking-force assisting apparatus, and may be decreased when the negative pressure in the first pressure chamber becomes smaller than the non-operating time preset negative pressure or the operating-time preset negative pressure.
Additionally, in the brake apparatus according to the present invention, the throttle-opening-degree control device may include normal-time conditioned throttle-opening-degree decreasing means for decreasing the degree of opening of the throttle valve when the braking-force assisting apparatus is normal and when the negative pressure in the first pressure chamber satisfies a predetermined condition.
According to this invention, the degree of opening of the throttle valve is decreased by the abnormal-time throttle-opening-degree decreasing means when the braking force assisting apparatus is abnormal, and the degree of opening of the throttle valve is decreased by the normal-time conditioned throttle-opening-degree decreasing means when the braking-force assisting apparatus is normal. The normal-time conditioned throttle-opening-degree decreasing means may include at least one of the limited-time opening-degree decreasing means, the large-change-time opening-degree decreasing means and the operating-time opening-degree-decrease suppressing means.
In a case in which the braking-force assisting apparatus increases a braking force after the pressure in the second pressure chamber reaches substantially an atmospheric pressure, a frequency of operations of the braking-force assisting apparatus can be decreased if the boost limit of the vacuum booster is increased by decreasing the degree of opening of the throttle valve when the braking-force assisting apparatus is normal. Thus, when the braking force assisting apparatus includes a pump, an operating noise of the pump can be reduced.
Additionally, there is provided according to another aspect of the present invention a brake apparatus adapted to be provided in a vehicle having an internal combustion engine, the brake apparatus comprising:
a vacuum booster having a first pressure chamber and a second pressure chamber, the first pressure chamber being connected to an intake pipe of the engine on a downstream side of a throttle valve, the second pressure chamber being selectively connectable to one of the first pressure chamber and atmosphere, the vacuum booster boosting an operating force applied to a brake operating member based on a pressure difference between the first pressure chamber and the second pressure chamber so as to output the boosted operating force to a master cylinder;
a brake cylinder operated by a fluid pressure generated by the master cylinder;
a pressure-increasing device increasing a fluid pressure provided to the brake cylinder to be greater than the fluid pressure generated by the master cylinder; and
a throttle-opening-degree control device controlling a degree of opening of the throttle valve, the throttle-opening-degree control device including abnormal time throttle-opening-degree decreasing means for decreasing the degree of opening of the throttle valve, when an abnormality occurs in the pressure-increasing device, so as to increase a negative pressure in the first pressure chamber.
The above-mentioned pressure-increasing device can be a braking-force assisting apparatus which increases a braking force after the vacuum booster reaches its boost limit or an emergency-time braking-force assisting apparatus which increases a braking force at an emergency time. It is preferable that in a case in which the emergency-time braking-force is used, when the emergency-time braking force assisting apparatus is abnormal, the negative pressure in the first pressure chamber be set to be greater than a non-operating-time preset negative pressure used when a braking operation is not being performed. This is because a braking force can be increased when a large operating force is applied by a driver at an emergency time.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.